x86: always supply .cpuid() handler to x86_emulate()

x86: always supply .cpuid() handler to x86_emulate()

With us incremementally adding proper CPUID checks to x86_emulate()
(see commit de05bd965a ["x86emul: correct {,F}CMOV and F{,U}COMI{,P}
emulation"]) it is no longer appropriate to invoke the function with
that hook being NULL, as long as respective instructions may get used
in that case.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>